The NSW Department of Education has sacked the teacher who taught the wrong maths course to HSC students from the beginning of the year.
The casual maths teacher had been working in a temporary position at Coonamble High School in NSW's north-west since term one.
However, parents at the school said that other people who were involved also "need to take responsibility".
"It comes down to who his supervisors were and how that works up the chain of command," Lee O'Connor, whose daughter was taught the wrong course, said.
"I was pretty upset at the beginning, pretty upset that it happened," said Mrs O'Connor, who is also president of the school's P&C.
"But things happen in life and you just have to deal with it. One would hope [the teacher] would learn a lot from this."
The department did not comment on whether the teacher will retain his accreditation and remain on the casual database.
It was revealed on Wednesday that he had been teaching two year 12 students and five year 11 students mathematics general 1, a course that does not count towards HSC or ATAR requirements, instead of mathematics general 2 for more than seven months.
The error was discovered less than two months before HSC exams begin in October, and the department and NSW Education Standards Authority are now arranging extra support for the students to catch up in time for this year's mathematics general 2 exam.
A spokesman for NESA said its maths inspector would arrive at the school tomorrow to "support the students [in preparing] for the exam".
They have also been told that they can choose to sit the exam again next year, a solution that NSW Education Minister Rob Stokes has deemed unacceptable.
"One of the solutions offered was if they don't do well they can do it again next year," Mr Stokes told radio 2GB on Thursday.
"That's clearly a laughable solution ... I'm angry on their behalf, if this was my child I would be furious."
Mrs O'Connor said her daughter, who is in year 11, is worried about how the mistake will affect her ATAR.
"The principal rang us last Friday morning," Mrs O'Connor said. "I understand it was picked up on Wednesday evening and they investigated it on the Thursday.
"We'd want to be assured it can never happen again and the department's taking the appropriate steps to make sure that that doesn't happen."
She said that the school is looking at alternative pathways to get into university for the year 12 students who have been affected.
"They're looking at options for principal's recommendations and early entry," Mrs O'Connor said.
"All the parents are concerned this would reflect quite badly on the school but we have brilliant teachers who go above and beyond," Mrs O'Connor said.
A spokesman for the department said it has launched "a thorough investigation of the circumstances, including the roles of staff with responsibilities for teaching and HSC procedures".
"As soon as the executive principal identified that the correct mathematics course was not being taught, her immediate priority has been to provide comprehensive support to students," he said.
A NESA spokesman said the students will not need to re-take school-based assessments and their existing marks from the incorrect course will be used towards their final HSC mark.